Method of and means for neutraliz



Dec. 26, 1950 M. CAMRAS Re. 23,311

1 METHOD OF AND MEANS FOR NEUTRALIZING INDUCTIVE DISTURBANCES IN MAGNETIC REPRODUCERS Original Filed Nov. 18, 1942 7 30 D Fil/l 2/ CL .ZZ'TUEWZZF M42 v//v CAME/46 Reissued Dec. 26, 1950 w?) 7 R UNITED STATES PATENT oFncE;

METHOD OF AND MEANS FOR 'NEUTRALI Z- ING INDUCTIVE DISTURBANCESIN MAG-' NETIC REPRODUCERS Marvin Cami-as, Chicago, IlL, assignor to Armour I,

Research Foundation of Illinois Institute of Technology, a corporation of Illinois 2 Claims.

(cine-100.2)

Matter enclosed in heavy brackets appears in" the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue This invention relates to improvements in a method of and means for neutralizing inductive disturbances in a magnetic reproducing or magnetic recording device so that only the inductive be oriented until the hum pick-up is at a minimum but this will not eliminate the hum pick-up from stray magnetic fields completely except under certain special' conditions which very rarely impulses created by a, magnetized recording occur in practice, namely, a single point source medium will be amplified and reproduced, while of alternating current magnetic fields, or several inductive disturbances resulting from stray magsources which give the fundamental components netic fields in the vicinity of the reproducing eleall in time phase, and harmonic components also ment or initial pick-up element will be neutralin time phase and in the same direction as the ized and balanced out, whereby fidelity of repro- 1o fundamental components. With a resultant duction is maintained. field that varies continuously as to both direction The invention is highly desirable for use in and magnitude, it is substantially impossible to connection with a magnetic recording and reorient the reproducing magnet to reduce the hum producing device wherein sound is recorded by pick-up. magnetizing an elongated recording medium In addition, it may be mentioned that the such as a paramagnetic tape or paramagnetic above two methods are not always practical with round wire. Frequently the recording device may certain types of magnetic record playing devices also be used as a reproducing device to reproduce for mechanical and practical reasons. For exwhat has been magnetically recorded on the ample, where the same magnet device is used to elongated medium. In other cases, one may be magnetize a wire or other elongated recording used for reproduction only. The instant invenmedium, and then later used as the pick-up magtion is designed to make that reproduction of net for reproducing a recording previously made greater fidelity by the neutralizing of inductive on that medium, it is not feasible to change the disturbances resulting from stray magnetic position of this magnet device, because the travel fields. of the wire through the machine is along a sub- In such a magnetic reproducing device, there stantially fixed path. is usually an amplification circuit, a driving .With the foregoing in mind, it is an important motor, power transformer, and other electrical object of the present invention to neutralize inelements used in the various circuits, such as a ductive disturbances resulting from stray magchoke coil, each of which may provide a stray 39 netic fields in 'a magnetic reproducer having a magnetic field which will also induce a voltage in pick-up magnet located in a fixed position, and addition to the voltage induced by the recording without effectively shielding the magnet. medium itself. While such stray fields will Another object of the invention resides in the theoretically resolve into a single resultant stray neutralization of inductive disturbances result field, such resultant'stray field is not always of ing from stray magnetic fields in a magnetic rethe same magnitude nor in the same direction, producer by the introduction of an auxiliary coil since other stray fields from various electrical in series with the pick-up or input magnet; or, if appliances or devices operating in the vicinity of so desired, the auxiliary coil may be in parallel the magnetic reproducer will likewise induce with the input or pick-up magnet. voltages in the pick-up elements, and these other 49 Another object of the invention is the eliminadevices may be turned on and off at indetermition of hum pick-up in a magnetic reproducer nate times, so that the ultimate resultant field in by the utilization of an auxiliary coil of approximost cases is continuously fluctuating as to both mately the same size and construction as the direction and magnitude. Consequently, in a pick-up magnet, and orienting the auxiliary coil magnetic record player, wherein ,the input magrelatively to the pick-up magnet so as to balance net or pick-up magnet is designed to respond to out induced voltages from stray fields. minute magnetic variations along a fine wire or A further feature of the invention resides in other elongated recording medium, the stray the provision of an auxiliary coil in the input hum pick-up may at times be even greater than amplification circuit of a magnetic reproducer the signal voltage from the wire. Of course, 50 to balance out inductive disturbances resulting there are two remedies for stray hum pick-ups. from stray magnetic fields. One is to enclose the magnetic input device or Still another feature of the invention resides pick-up device in a shield, but this remedy is exin the introduction of an auxiliary pick-up coil tremely costly if done effectively. Second, the in a location in close proximity to the input or magnetic pick-up device or input device might pick-up 'magnet of a magnetic reproducer, for

the purpose of balancing outdisturbances from Stray magnetie fieias A further Ieature of the invention resides in the provision of a hum reducing arrangement including the use of an auxiliary pick-up device in a region where the magnetic fleld is substan tially an image or the field near the majorpick f up device in respect to stray field conditions, and

orienting the auxiliary pick updevic'ef'so as to vision oi a, new and novel method-of eliminating, a neutralizing, or balancing out theinductive disturbances resulting from stray magnetic -fields, in connection with a magnetic reproducing device.

While some of the more salient features, characteristics and advantages of theinstant invention have been abovepointed out, others willibe come apparent from the following disclosures, taken in conjunction with'the'accompa'nying drawing, in which? Figure 1 is 'a, fragmentary "front elvatioiial view 01 a, magnetic recording and reproducing device, equipped with means embodying-the principles of the instant invention and incorporating the practice of mynovel-niethcd-initsuse;

Figure '2 is a simplified diagram-or the input portion of the amphfying'eircuit; embodiedin the device of Figure 1, and 'alsoincluding principles of the instant inventionifand' Figure "3 is anothersimpliiied diag'iam of the same portion of the amplifying circuit as Figure 2, but illustrating a difierent connection' for the auxiliary pick-up coil.-

As shown on stemming:

The illustrated embodiment of the instant invention is shown associated-with *a magnetic recording and reproducing device including a cabinet orother supportingstructure-5 having a front panel "6 carriedjthe'r'eby; 'All of 'the operating equipment of the recording and reproducing device which need "be described-herein may be carried or supported .by'thep'anelfi.

Near one side of the panel a reel 'or'spool I is rotatably mounted, and near'theoppositeside a similar reel 8 is 'rotatablymounted. These reels may be operated "in both'directionsso to wind a recording "medium 'backwardand"forward'therebetween in 'eithendirection. In the present instance,'the recordingmediurn' is'show-n in the 'form'of avery 'fineround "wire 9, which may be of approximatelythe size of'a hu'rrian hair, '.004' or .005 inch in diametenbeing satisfactory.

With the illustrated recording and reproduc ing device, therecording'me'diumor'wire 9'travels from reel 1 to reel 8' duringthe'nialiing'ofa're the instant inventicncenters itself mainly housing-13," around another guide pulley "through'a level'w'ind arrangement I5, and onto a 4 the "reproduction operation of g'the :device. It is nonessential-shat the d'ev ice -beI- madeto both record and reproduce, but such is a convenient form.

Astheswire travels from reel 7 to reel :8 it first passes through a level wind element In assosat s-wan reel 1 thence through an erasing head i I designed to demagnetize the wire, around a guide pulley through a recording head in a I4,

reel 8:

During-e: reproduction from a wire previously magnetized;: the erasing head ll does not function, and the recording head in the casing I3 acts as the reproducing or pick-up magnet which may for convenience be termed the input magnet of the amplifying -circuit. With reference to Figure 2, it will be seen that this input magnet-includes a paramagnetic core I6, preferably laminated, havinga relatively minute air gap 11 to establish in effect pole pieces of oppositepolarity *on each side 'of "the air gap; Around one portion "of the core 16a windingor coil I8 is positioned. It willjthereforejbe'seen'that duringa reproduction, as the'wire epassesover-or through a slot in the pole pieces 'on eachside of the air -gap H, the magnetization onthiswirewill induce a voltage in the coil"'l8;andfthis' induced-voltage will vary in accordancewith the-varying mag-'- netization of the wire.

Other voltages from"stray"'magneticfie1ds in the vicinity will'also he induced in the coil 1 8,and

in view of the fact "thattlii's coil connected in the input poftion of the amplifying "circuitfit is desirable to "neutralizeo'rb-alance (iii the "effect' of the induced voltage from strayfiel'ds, and such is efficiently accomplished by the instant inventi'o'n.

' With reference to Figure2, it will be seen that thecoil'lB fis connected'atone end througha conductor l9 to thegridpf anamplifying tube 20 which is diagrammatically illustrated' 'as -a trio'de, whe'reasun practice, a pentode "including both screen and suppressor grids would 'p'robably'be used, since'this tubeforin's the first stage of amplification. A unicell battery 21 nlay be inclined "in the" conductor l9 'as'a' grid" bias The other "end of "the'coil" I8 "is connected "through-e conductor "22 to a coil"23 whi'chis in "the 'form of "an auxiliary pick' upmoil {and preferablyis approximately the "same construction and *the same number of turns asthe coil I'8. Inthis illustrated "instance, the auxiliary pick-up coil 23 is in'series' with the coill8, and'theopposite end of the'coil 23 is connected through'a conductor 24 "to'a source"of energyi'such'as "a battery- 25. The cathode o'f the tube '20 "may be connected through conductor 25 to the'conducto'r M. The plate of the tube'zll "is connected through""con'- duct'or 21 to a load"'resist'ancef28which in *turn is connected-as indic'atedat 29 tothe'opposite side of the battery "25." 'Thus, we'have a simplified input portion 'of an amplifying circuit, including the" first stage of amplification, and further 'stages'of 'ar'nplifieati'onmay be connected as indicated by"extendedconductors 30 and '3l, a condenser 32 preferably beingincluded in the conductor 30.

Inoperation, the pick up coil 8 willnot' only have a voltage inducedth'erein'byvirtue of'the magnetized wire 9, "but will also have another varying voltage'induced by'the resultant of stray magnetic fields; These stray 'magneticfieldsinay originate in a power transformer, driving motor, choke coil, and similar apparatus used in the magnetic reproducing device itself. Likewise, there may be additional stray fields from electrical apparatus operated in the vicinity of the magnetic reproducing device. If the resultant of all these stray fields was constant, the pick-up or input magnet still could not be oriented effectively because by virtue of the travel of the wire 9, this magnet must remain substantially in fixed position.

The auxiliary pick-up coil is, therefore, used, and this coil is preferably placed as closely as possible to the coil IB so as to be in a region of stray magnetic fields which is an image of the region in which the coil [8 is located. As seen in Figure l, the coil 23 is positioned as closely as possible to the coil I8, this being the preferable location. With such positioning, any voltage induced by a stray field in the coil 18 will likewise be induced by the same field in the coil 23, and the resultant stray field will have the same effect on the coil 23 as it does on the coil l8, and will be of the same magnitude and the same direction as to both coils.

The coil 23 is oriented to cancel or balance out the voltages induced from stray fields, and this orientation may be by opposite connection, opposite winding, or in some other suitable manner. In the illustrated instance, the coil 23 is oppositely wound to the coil I8, and, therefore, the voltages induced by stray fields in the coil 23 will be in opposition to the voltages induced by the same stray fields in the coil I8, and thus there is a balancing out of all inductive disturbances resulting from stray fields. The voltage induced in the coil l8 by the magnetized wire or recording medium will not be induced in the coil 23 by virtue of its position, so the result will be a true and accurate amplification of the inductive impulses from the magnetized recording medium alone, namely, fidelity of reproduction without any hum or other noise resulting from stray field disturbances.

Of course, voltages induced in the coil l8 by the magnetized recording medium will disrupt the bias on the grid of the tube 20, amplification of these impulses will result, and the amplification may be reproduced at audio frequency through a loud speaker, all in a manner known to those skilled in the art.

The coil 23 does not of necessity have to be connected in series with the pick-up or input coil l8. In Figure 3, I have illustrated substantially the same simplified diagrammatic showing of an input portion of the amplifier circuit as is illustrated in Figure 2. The same reference numerals have been used to designate like parts, but in this instance the conductor 22 is eliminated, and conductor 24 runs direct from the battery to one side of the pick-up or input magnet coil 18. The auxiliary pick-up coil 23 is shown connected between conductors l9 and 24, in parallel with the coil l8. With this arrangement, it will be seen that the hum balancing or auxiliary pick-up coil 23 is in a region of stray fields which is the exact image of the region of stray fields occupied by the coil l8. Again, the coil 23 is oriented by being wound oppositely to the coil l8, so that voltages induced by stray fields in the coil l8 will be neutralized by equal and opposite voltages induced by the same stray fields in the coil 23.

My novel method of neutralizing inductive disturbances in a magnetic reproducing device is believed suficiently apparent from the foregoing as not to warrant further detailed description herein.

From the foregoing, it is apparent that I have provided novel means and a novel method 'of neutralizing or balancing out inductive disturbances occurring in the input circuit of a reproducing device. It is apparent that by the aid of an auxiliary coil, properly oriented, and arranged to oppose stray pick-up of the magnetic input device, inductive disturbances resulting from stray magnetic fields may be balanced out of the magnetic input device, leaving only the effect of the intended and proper magnetic field to be amplified. It is further apparent that my novel arrangement is simple in construction, and extremely economical to incorporate in a magnetic reproducing system and to operate.

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

[l. In a device for reproducing magnetic recordings, an input magnet responsive to magnetic variations along an elongated recording medium, said magnet having a coil, and an auxiliary pick-up coil connected in circuit with the magnet coil and arranged to substantially neutralize the effect of stray voltages induced in the magnet coil regardless of the general location 'of said device] a 2. In a magnetic reproducing device, a panel,

a pair of spaced reels thereon, an elongated re-.

cording medium on said reels, a reproducing head including an electromagnet [between said reels in the path of said recording medium] having a pair of poles spaced longitudinally of said medium and both on the same side thereof and across which said medium travels and a pick-up coil on said panel immediately adjacent the coil of said electromagnet in permanent circuit connection therewith and orientable to substantially neutralize the effects of stray voltages induced in said electromagnet regardless of the general location of said device.

[3. The method of neutralizing inductive disturbances in a pick-up magnet for a reproducer of magnetic recordings, including the step of setting up a reactionary inductance by an induction coil located in a region of stray magnetic fields which is an image of the stray magnetic region of said pick-up magnet and orienting said induction coil with respect to said pick-up magnet to balance out the efiects of a particular stray magnetic field region of the pick-up magnet depending upon the location of the apparatus.]

[4. In a device for reproducing magnetic recordings, an input magnet responsive to magnetic variations along an elongated recording medium, said magnet having a coil, and a hum bucking coil connected in circuit with and disposed adjacent said magnet coil and orientable to substantially neutralize the efiects of inductive disturbances in said magnet caused by sources foreign to said device and apparatus connected therewith] [5. The method of neutralizing inductive disturbances in a pick-up magnet for a reproducer of magnetic recordings caused by stray fields from sources external-to thereproducer and. its associated :apparatus, including the steps 'of setting up an opposing inductance by an intimation coilii'n -.circuit with said pick-up magnet, and orienting :said coil to balance out the effects of said stray fields] 6. In a device for reproducing magnetic recordings, an input magnet responsive to magnetic variations along'a'path of movement of a recording medium, said magnet having a'pair 10 of poles spaced longitudinally "of said path of movement =of.,said recording medium with both poles on the asame-sideithereof and across which said medium travels, said magnet also having a coil with a straight amis, and asecondpick-up coil with a straight axis of approximately the same size and construction as said first mentioned coil and connected in circuit with said first mentioned coil and positioned with its "said axis-parallel ;to and laterally spaced alongside of-said axis ofisaidfirst mentioned :coil, said recoil-s being immediatelyv adjacent each other insidebye-side relationship :said second vmentioned =c0il being connected :to asaid first mentioned coil at all times to substantially neutralize the efiect of stray voltages induced in said first mentioned coil regardless ofthe location. of saiddeoice.

\ 'ClA-MRAS.

REFERENCES CITED The following references are of record in :the file of this patent or the original patent:

FOREIGN PATENTS Number Country Date 457,282 Germany Mar. :13, 1928 622,623 Germany s Dec.v2, 1935 

